1. Field of the Invention
The present invention relates to a non-emissive material of Formula 1 and a composition including the same for fabricating an organic electroluminescent device.
2. Description of Related Art
Organic light-emitting devices (OLEDs) are gaining attraction in the recent years as the active displays owing to their characteristics such as high brightness, quick refresh rate and wide color gamut and are more suitable for portable electronic applications.
In general, an OLED includes an anode, a hole transport layer, an emitting layer, an electron transport layer and a cathode, which are deposited one over the other sequentially, by means of vacuum deposition or coating techniques. When a voltage is applied, the anode injects holes and the cathode injects electrons into the organic layer(s). The injected holes migrate to the emitting layer through the hole transporting layer and the electrons migrate to the light emitting layer through the electron transporting layer. In the emitting layer, the holes and electrons recombine to produce excitons. Light is emitted when the exciton relaxes through a photoemissive mechanism.
The reason for manufacturing an organic electroluminescent (EL) display with a multi-layered thin film structure includes stabilization of the interfaces between the electrodes and the organic layers. In addition, in organic materials, the mobility of electrons and holes significantly differ, and thus, if appropriate hole transporting and electron transporting layers are used, holes and electrons can be efficiently transferred to the luminescent layer. Also, if the density of the holes and electrons are balanced in the emitting layer, luminous efficiency can be increased. The proper combination of organic layers described above can enhance the device efficiency and lifetime. However, it has been very difficult to find an organic material that satisfies all the requirements for use in practical display applications.
The initial OLEDs used emissive materials that emitted light from their singlet states, termed as “fluorescence”. Fluorescent emission generally occurs in a time frame of less than 10 nanoseconds. Several OLED materials and device configurations utilizing fluorescence are described in U.S. Pat. No. 4,769,292, U.S. Pat. No. 5,844,363, and U.S. Pat. No. 5,707,745, which are incorporated herein by reference in their entirety.
More recently, OLEDs having emissive materials that emit light from triplet states (“phosphorescence”) have been demonstrated in literature, Nature, 1998, No. 395, p. 151 and Appl. Phys. Lett., 1999, No. 3, p. 4, and patent document U.S. Pat. No. 7,279,704, which are incorporated herein by reference in their entirety.
For a high luminous and efficient phosphorescent OLED's, a host material must have non-emissive high triplet energy and a balanced electrical charge (hole/electron) injection/transport characteristics. Moreover, the host material should also possess good electrochemical stability, high thermal resistance and excellent thin film stability. However, compound capable of satisfying all the said properties from practical considerations have not been known till date.
Patent documents such as WO2003-78451, WO2005-76668, US2006-51616, JP2008-280330, WO2008-123189, JP 2009-21336 Attempts have shown materials having excellent bipolar transport characteristics; however, due to mismatch of the energy levels of the molecular orbitals with the adjacent layers in the organic electroluminescent devices, the challenges still remain in achieving high efficiency and good device stability.